The present invention is directed to a high speed ultrasonic signal processing system that captures all of the ultrasonic signals necessary for an ultrasonic inspection and, more particularly, to a system that uses paired flaw gates where each flaw gate processes data during a time window that corresponds to depth within the material being inspected and the data collected by one of the flaw gates in the pair is transferred to a central control and flaw location computer while the other flaw gate in the pair processes incoming ultrasonic signal data.
In a computerized ultrasonic inspection system, in general, the limitations on incoming signal processing speed also limit the speed at which an inspection of an object such as a power plant turbine rotor can be conducted. Volumetric ultrasonic inspections must sweep an ultrasonic beam through the entirety of the material being inspected to obtain complete coverage. If the size of the flaws to be detected is very small, a small ultrasonic beam is required involving a substantial number of beam passes through the material to detect all the flaws. The total time required for an inspection is a major factor in the cost of examining objects such as turbine rotor bores. Inspection of turbine rotor bores at the end of the manufacturing process as well as during periodic routine maintenance is required to detect flaws near the bore surface that can be removed by remachining or to detect deeper flaws that must be monitored to determine their changes so that the rotor can be removed from service before a catastrophic failure occurs. Reduced inspection time is thus particularly desired by power generating utilities.
A significant factor which limits the speed of rotor inspection is the time required to record the data associated with ultrasonic indications which when found can indicate a flaw. An ultrasonic indication is a reflection signal received by a transducer which exceeds an amplitude threshold level established during a calibration procedure. A flaw gate is used to establish the minimum and maximum transit time intervals between which data will be processed as well as to compare the return signal data to the amplitude threshold. A conventional flaw gate is essentially a windowed threshold comparator used on a returning echo signal which allows only ultrasonic indication signals to pass through for further processing. The signal is passed when it is within the time window and exceeds the amplitude threshold. For each indication it is necessary separately to record the amplitude of the indication, the time of flight of the pulse producing the indication and the position coordinates of the transducer within the rotor reference frame at the time the indication is detected. When the above data are combined with knowledge concerning the path geometry of the ultrasonic beam, the location of the reflector or flaw as well as its size can be determined.
In conventional computer operated ultrasonic inspection systems the computer must read not only the status of the ultrasonic instrumentation devices but also the position of the transducer. If an indication is recorded, the single computer stores a record of the time of the indication along with the scanner position. This conventional scheme becomes highly inaccurate and data may be missed if the scan speed is so rapid that the main computer is not able to keep up wth the rate at which data comes from the transducer.